MAGNETIC-FIELD DEPENDENT QUANTUM FLUX-CREEP IN BI2SR2CA2CU3O10

We have performed magnetization-relaxation measurements as a function of temperature and magnetic field in bulk and powdered Bi2Sr2Ca2Cu3O10 compound samples. At low temperatures the quantum tunneling of Abriko sov vortices could be clearly observed as well as its T2 thermally ass isted temperature dependence. The tunneling rate is observed to increa se with the applied magnetic field reflecting the reduction of the col lective pinning length. When the 3D-to-2D dimensional crossover of the vortex ensemble occurs both the pinning length and the tunneling rate saturate.